We are investigating and further characterizing the RNA metabolism of cells infected with RNA tumor viruses. Most of the experiments involve mouse cells infected with murine leukemia virus (MuLV), and in some cases other cells and other RNA tumor viruses will be used. Virus-specific RNA in these experiments is detected by RNA-DNA hybridization of cellular RNA with virus-specific DNA synthesized by the "endogenous" reverse transcriptase reaction in MuLV. Three topics are being studied: 1) DNA sequence analysis for the region of the MuLV genome encoding the gag proteins is being performed. 2) Virus-specific mRNAs are being examined for the presence of "spliced" sequences by S1 nuclease mapping using cloned MuLV DNA restriction fragments. 3) Attempts to clone virus-specific mRNA are in progress.